Is anyone waiting for the other dreaded shoe to drop?

I hope they do.

Yes, Mary lives for a long time yet before she's executed, more than enough time for the show to run its course. Season 3 finale spoiler, I think they squeezed in the circumstances of the real Mary's execution by passing them on to Lola. The drama of being accused of being involved in a plot to assassinate Elizabeth and then being executed by beheading was probably too juicy to pass up and since they play fast and loose with the history anyway, (unless it's a major point, such as when one of the major, real players like Francis, actually dies) they had no problem including that as a way to write Lola out.

Mary's son James took the throne after Elizabeth's death, I thought that interesting. He ruled over England and Scotland both, and Ireland too if I remember correctly. Someone who was with Elizabeth when she died believed that Elizabeth stated to them somehow that she wanted James to succeed her on the English throne, as she had no heirs herself.

That is likely, though with enough notice(which unfortunately doesn't happen often enough with shows), they will have time to plan. I think I could see them doing something like a flash forward to Mary's death in the last episode.